In the drawings of the machining industry, some thread codes are often seen. Do you know what they mean? Now let's learn.

The code of the common thread of the pipe joint and their matching relationship

BSPT and BSP----British Specification Taper Thread 
NPT----US Spec Taper Thread
PT----Japan's old JIS standard taper thread, equivalent to ISO standard R, Rc
DIN2999----Europe is mainly German pipe thread

NPT
NPT is the American standard taper pipe thread for general use.
Where N means National (American) American National Standard, P means PIPE , T means TAPER , and the profile angle is 60°.
This type of pipe thread is commonly used in North America, or is often seen in the use of ANSI codes. National standards can be found in GB/T12716-1991
We must pay attention: NPT teeth must be used in the ANSI specification!

PT
The PT tooth is an inch taper thread with a tooth angle of 55°, which is the most commonly used in sealing. It is mostly used in Europe and the Commonwealth of Nations. In fact, the JIS standard in Taiwan and Japan also follows the British standard, and China actually uses the British screw thread. It belongs to the Wyeth thread family. Chinese national standards can be found in GB/T7306-2000.
The inch pipe thread is a fine thread, because the thread depth of the coarse thread is large, which will seriously reduce the strength of the pipe with the outer diameter of the thread cut.
In addition, in the actual pipeline with small diameter, NIPPLE is often used. The purpose is that the wall thickness of the purchased NIPPLE is relatively thick, which can ensure the strength of the tapping part, and the main pipeline does not need thick pipe wall. To save costs.
PF teeth are parallel threads for pipes.
We must pay attention: PT teeth and so on must be used in the JIS specification!

G
G is a 55 degree non-threaded sealing pipe thread, which belongs to the Whitworth thread family. Marked as G stands for cylindrical thread. Chinese national standards can be found in GB/T7307-2001
G is the general name for pipe threads (Guan), and the division of 55 and 60 degrees is functional, commonly known as pipe circle. That is, the thread is machined from a cylindrical surface.

ZG
ZG is commonly known as pipe cone, that is, the thread is processed by a conical surface, and the general water pipe joint is like this. The old Chinese national standard is marked as Rc.
Metric threads are represented by pitch, American and British threads are represented by the number of threads per inch, which is the biggest difference between them. Metric threads are 60-degree equilateral teeth, inch threads are isosceles 55-degree teeth 60 degrees.
Metric threads are in metric units, American and British threads are in imperial units.
Pipe threads are mainly used to connect pipes, and the inner and outer threads are closely matched, and there are two types of straight pipes and tapered pipes. Nominal diameter refers to the diameter of the connected pipe, obviously the major diameter of the thread is larger than the nominal diameter. 1/4, 1/2, 1/8 are the nominal diameters of imperial threads in inches.

Identification of inch uniform threads
The inch uniform thread is widely used in countries where the inch system is used. This type of thread is divided into three series: coarse thread series UNC, fine thread series UNF, extra fine thread series UNFF, plus a fixed pitch series UN.
Marking method: thread diameter—number of teeth per inch Serial code—accuracy grade
Example: Coarse Tooth Series 3/8—16 UNC—2A
Fine tooth series 3/8—24 UNF—2A
Extra fine tooth series 3/8—32 UNFF—2A
Fixed pitch series 3/8—20 UN—2A
The first digit 3/8 represents the outer diameter of the thread, in inches. To convert to the metric unit mm, multiply by 25.4, that is, 3/8×25.4=9.525mm; the second and third digits 16, 24, 32, and 20 are The number of teeth per inch (the number of teeth on the length of 25.4mm); the text code UNC, UNF, UNFF, UN after the third digit is the series code, and the last two digits 2A are the accuracy grade.

Conversion of 55° Cylindrical Pipe Thread
The 55° cylindrical pipe thread comes from the inch series, but it is widely used in countries using the metric and inch systems. It is used for the connection of pipe joints and pipes for transporting liquids, gases and installing wires. However, the codes of different countries should be used. The foreign codes in the following table (comparison table) are converted into Chinese codes, and the 55° cylindrical pipe thread codes of various countries are listed in the following table.
Country code
China G
Japan G, PF
UK BSP, BSPP
French G
Germany R (internal thread), K (external thread)
Former Soviet Union G, TPУБ
ISO Rp

Conversion of 55° Conical Pipe Thread
55° conical pipe thread means that the thread angle is 55° and the thread has a taper of 1:16. This series of threads is widely used in the world, and its code name varies from country to country, see the table below. Convert the foreign code in the following table to the Chinese code.
Country code
China ZG, R (external thread)
British BSPT, R (external thread), Rc (internal thread)
France G (external thread), R (external thread)
Germany R (external thread)
Japan PT, R
ISO R (external thread), Rc (internal thread)

Conversion of 60° Taper Pipe Thread
60° tapered pipe thread refers to the pipe thread with a profile angle of 60° and a thread taper of 1:16. This series of threads is used in the Chinese machine tool industry, the United States and the former Soviet Union. Its code name, China used to be K, and later it was Z, and now it has been changed to NPT. See the table below for the thread code comparison table.
Country code
China Z (old) NPT (new)
US NPT
USSR B

Conversion of 55° trapezoidal thread
Trapezoidal thread refers to a metric trapezoidal thread with a profile angle of 30°. This series of threads is relatively uniform at home and abroad, and its codes are quite consistent. See the following table for thread codes.
Country code
China T (old) Tr (new)
ISO Tr
Germany Tr
former soviet union tr

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